This invention relates to a method and apparatus for measuring sound that takes into consideration age-based and individual hearing characteristics.
Human auditory sensitivity to sound differs according to frequency. Thus, in the measurement of sound, it has been proposed to measure sound pressure level to which is applied a frequency weighting that simulates the hearing characteristics. Starting from the 1930s, what is termed xe2x80x9cA-weighting characteristicxe2x80x9d frequency correction circuitry has been incorporated into sound level meter standards in America, Germany and other countries, one after another. In Japan, too, current sound evaluation methods prescribe evaluation using xe2x80x9csound level weighted with an A-weighting characteristic frequency correction circuitxe2x80x9d (JIS Z8731 xe2x80x9cMethods of measurement and description of A-weighted sound pressure levelxe2x80x9d and ISO 1996/1 xe2x80x9cSoundxe2x80x94methods of describing and measuring environmental noisexe2x80x94Part 1: Basic quantities and how to obtain themxe2x80x9d).
The existing sound-level meter standards, JIS C1502 xe2x80x9cSound-level metersxe2x80x9d and JIS C1505 xe2x80x9cPrecision sound-level meters,xe2x80x9d stipulate the incorporation of A-weighting characteristic (frequency characteristic of FIG. 3) frequency correction circuitry and the ability to display the measurement values (sound level, dB). Also, in recent years, sound level meters (loudness meters) are being sold in Japan and overseas that not only correct the frequency characteristics, but also provide a more accurate display of the loudness of a sound (loudness), based on the ISO standard xe2x80x9cISO 532, Method B.xe2x80x9d
FIG. 4 shows an example of an apparatus for measuring sound pressure level predetermined in the Japanese method of evaluating sound. Reference numeral 1 denotes a microphone, 2 a level adjustment circuit, 3 a frequency correction circuit, 4 a squaring circuit, 5 an integration circuit, 6 a leveling circuit, and 7 an indicator. The microphone 1 converts measured sound pressure to an electrical signal, the level adjustment circuit 2 changes the gain of the signal input from the microphone 1, and the frequency correction circuit 3 is a circuit that applies to a measured sound pressure signal P a frequency weighting that simulates the hearing characteristics, as described above, such as for example a circuit that has the A-weighting characteristic of FIG. 3. The squaring circuit 4 squares the A-weighting characteristic-corrected sound pressure PA, and the integration circuit 5 is a circuit for smoothing the squared sound pressure signal PA2. In the leveling circuit 6, the root-mean-square of the sound pressure of the smoothed signal is converted to a logarithmic value (dB value), which is displayed by the indicator 7. Typical evaluation quantities are listed in Table 1 of JIS Z8731. For example, A-weighting characteristic sound pressure level LpA is expressed as 10 log10 PA2/P02 (here, for the reference sound pressure P0, 20 xcexcPa is used, which is close to the sound pressure of the minimum sound that can be heard by a young person with sound hearing).
The measurement value of a sound subjected to A-weighting characteristic sound pressure level hearing correction or the like, or calculated loudness value, corresponds well to the loudness of a sound actually perceived by a person. However, this is only the case when the subject is a young person with normal hearing. Moreover, when hearing characteristics are altered by hearing impairments or aging, there is never a good correspondence with the audible loudness.
FIG. 5 shows a typical example of aging-based changes in audibility. In FIG. 5, horizontal axis values represent time and vertical axis values represent relative amplitude. The sound of the upper half of FIG. 5(a) is an example of the sound of a large bus with many low-frequency components, corrected using a conventional A-weighting characteristic correction circuit, and the sound of the upper half of FIG. 5(b) is an example of the sound of a sawing machine containing many high-frequency xe2x80x9cscreaming soundxe2x80x9d components, also corrected using a conventional A-weighting characteristic correction circuit. These are simulations of the sounds a young person with sound hearing hears. In contrast, the lower halves of FIGS. 5(a) and 5(b) are simulations of the sounds an aged person hears.
In the case of sounds with many low-frequency components such as the sounds of FIG. 5(a), there is no major difference between what is heard by young people and aged people. However, in the case of sounds with many high-frequency components such as the sounds of FIG. 5(b), there is a major difference between what is heard by young people and aged people. Thus, in accordance with differences in the types of sounds (the frequency components contained therein), there are sounds that aged people hear as small sounds owing to changes in their hearing characteristics and as louder sounds to the same extent as heard by young people (see FIG. 5; the same problem arises with respect to people with impaired hearing).
Warning sounds emitted by equipment, along with spoken announcements in public spaces and other such speech sounds, have to be properly audible to everyone. However, these sounds are not always audible to aged people whose hearing characteristics have changed, or to people with impaired hearing. However, because measurements taken with measuring devices (sound level meters) that use existing A-weighting characteristic correction circuits are based on the hearing characteristics (A-weighting characteristic) of young people, it is impossible to accurately measure such differences in the loudness of sounds as perceived by aged people or people with impaired hearing. There is therefore a limit with respect to an evaluation of the loudness of sounds that takes into consideration the hearing characteristics of people with hearing impairments.
Also, there are of course individual differences in hearing characteristics, but because, as described above, measurements made using existing measuring devices are based on average characteristics of young people with sound hearing, it has not been possible to properly cope with individual differences in hearing characteristics.
An object of this invention is to provide a method and apparatus for measuring sound that takes age-based and individual hearing characteristics into consideration and handles these hearing characteristics.
The present invention provides a method and apparatus for measuring sound corresponding to the hearing characteristics of a predetermined age, comprising reading out from a memory hearing characteristic data by age group, and using the hearing characteristics for the predetermined age to correct input sounds.
Since individual hearing characteristics differ, the present invention also provides a method and apparatus for measuring sound corresponding to individual hearing characteristics, comprising measuring individual hearing characteristics, calculating a correction value for reference hearing characteristics and using the correction value to correct input sounds.
The measurement apparatus of this invention includes one provided with selection means that can freely select hearing characteristic data by age group and individual hearing characteristic data.
As described in the foregoing, this invention measures input sounds that are corrected based on hearing characteristic data by age group or individual hearing characteristic data, thereby making it possible to accurately measure sounds corresponding to these hearing characteristics.